Modern wireless networks, such as paging systems, can readily be configured to offer a variety of telemetry services, notably fleet and asset management. The management of vehicles within a fleet as well as assets involves obtaining information, generally in real-time, about the location and movement of these objects. The fleet manager utilizes this information to maximize use of fleet resources. With the advent of the Global Positioning System (GPS) supported by a constellation of satellites, a vehicle may determine its location with great accuracy and convenience if no obstruction exists between the GPS receiver within the vehicle and the satellites. Additionally, in recognition of the utility of real-time location of vehicles, governmental bodies have begun to impose strict requirements for determining position information of emergency 911 callers. Therefore, with the impetus stemming from competitive and regulatory forces, service providers seek to offer an efficient, cost-effective fleet and asset management service with robust capability by effectively integrating GPS technology with wireless networks so as to minimize bandwidth in the exchange of telemetry data.
FIG. 11 shows a diagram of a conventional wireless network in an autonomous GPS environment. As shown, a wireless network 1101 communicates with vehicles 1103 to track the location of these vehicles 1103 within the coverage area of the wireless network 1101. Each of the vehicles 1103 employ a GPS device 1105 that communicate with a constellation of satellites 1107. These satellites 1107 transmit very low power interference and jamming resistant signals received by the GPS receivers 1105. At any point on Earth, a GPS device 1105 is able to receive signals from multiple satellites (e.g., 6 to 11).
A GPS device 1105 may determine three-dimensional geolocation from signals obtained from at least four satellites. Measurements from satellite tracking and monitoring stations located around the world are incorporated into orbital models for each satellite to compute precise orbital or clock data. GPS signals are transmitted over two spread spectrum microwave carrier signals that are shared by all of the GPS satellites 1107. The device 1105 must be able to identify the signals from at least four satellites 1107, decode the ephemeris and clock data, determine the pseudo range for each satellite 1107, and compute the position of the receiving antenna. The time required to acquire a position depends on several factors including the number of receiving channels, processing power of the receiving device, and strength of the satellite signals.
The above arrangement, as an autonomous GPS environment, has a number of drawbacks that can hinder its effectiveness as a fleet management system. Because the GPS device 1105 must obtain all of the ephemeris data from the satellite signals, weak signals can be problematic. A building location or a location in any area that does not have clear view of the satellite constellation 1107 can prevent the GPS device 1105 from determining its geolocation. Also, cold start acquisition may consume a few seconds to as much as a few minutes, which is a significant delay for the device's ability to log positional information and evaluate its position against pre-configured alert conditions.
The vehicles 1103 then need to transmit the location information to the wireless network 1101. These transmissions can consume large amounts of bandwidth of the wireless network 1101 if the location information is continually transmitted without attention to the polling scheme and the underlying transmission protocol used to transport such data. Additionally, conventional limitations on the amount of storage available on devices configured for tracking of vehicles 1103 constrain the amount of information that may be retained for communication with the wireless network 1101.
If one of the vehicles 1103 is in imminent danger, e.g., of losing its ability to communicate with the wireless network 1101 for some reason, it may not be able to transmit to the wireless network 1101 information needed for the wireless network 1101 to be able to respond to needs of the vehicle 1101 in a timely manner. This may be especially critical, e.g., if the vehicle 1103 is progressing into a state which may pose an imminent danger to occupants of the vehicle. Additionally, if the vehicle 1103 loses its ability to communicate with the wireless network 1101 for an extended period of time, it may be difficult to determine critical information which was available at the vehicle 1103, but had not been communicated, just prior to the loss of communication with the wireless network 1101.
Therefore, there is a need for a fleet and asset management system that prioritizes information to be sent from the vehicles 1103 to ensure timely acquisition of location information, while ensuring that urgent information is communicated from the vehicle prioritized over other information that is less urgent. There is also a need to maintain certain information that may be available to the vehicle 1103, but that has not been sent from the vehicle 1103 prior to a loss of ability to communicate with the wireless network 1101. There is also a need to efficiently utilize precious resources of the wireless network in support of fleet and asset management services.